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            <h2 class="title" style="clear: both"><a id="build_unix_notes"></a>Architecture independent FAQ</h2>
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        <ol type="1">
          <li>
            <span class="bold">
              <strong>I have gcc installed, but configure
                fails to find it.</strong>
            </span>
            <p> 
                Berkeley DB defaults to using the native C compiler
                if none is specified. That is usually "cc", but some
                platforms require a different compiler to build
                multithreaded code. To configure Berkeley DB to build
                with gcc, run configure as follows: 
            </p>
            <pre class="programlisting">env CC=gcc ../dist/configure ...</pre>
          </li>
          <li>
            <span class="bold">
              <strong>When compiling with gcc, I get
                unreferenced symbols; for example the following:
                <pre class="programlisting">symbol __muldi3: referenced symbol not found
symbol __cmpdi2: referenced symbol not found</pre></strong>
            </span>
            <p>
                Berkeley DB often uses 64-bit integral types on
                systems supporting large files, and gcc performs
                operations on those types by calling library
                functions. These unreferenced symbol errors are
                usually caused by linking an application by calling
                "ld" rather than by calling "gcc": gcc will link in
                libgcc.a and will resolve the symbols. If that does
                not help, another possible workaround is to
                reconfigure Berkeley DB using the <a class="link" href="build_unix_conf.html#build_unix_conf.--disable-largefile">--disable-largefile</a>
                configuration option and then rebuild. 
            </p>
          </li>
          <li>
            <span class="bold">
              <strong>My C++ program traps during a
                failure in a DB call on my gcc-based
                system.</strong>
            </span>
            <p> 
                We believe there are some severe bugs in the
                implementation of exceptions for some gcc compilers.
                Exceptions require some interaction between compiler,
                assembler, and runtime libraries. We're not sure
                exactly what is at fault, but one failing combination
                is gcc 2.7.2.3 running on SuSE Linux 6.0. The problem
                on this system can be seen with a rather simple test
                case of an exception thrown from a shared library and
                caught in the main program. 
            </p>
            <p> 
                A variation of this problem seems to occur on AIX,
                although we believe it does not necessarily involve
                shared libraries on that platform. 
            </p>
            <p> 
                If you see a trap that occurs when an exception
                might be thrown by the Berkeley DB runtime, we suggest
                that you use static libraries instead of shared
                libraries. See the documentation for configuration. If
                this doesn't work and you have a choice of compilers,
                try using a more recent gcc- or a non-gcc based
                compiler to build Berkeley DB.
            </p>
            <p> 
                Finally, you can disable the use of exceptions in
                the C++ runtime for Berkeley DB by using the
                <a href="../api_reference/CXX/envcreate.html#env_DB_CXX_NO_EXCEPTIONS" class="olink">DB_CXX_NO_EXCEPTIONS</a> flag with the <a href="../api_reference/CXX/env.html" class="olink">DbEnv</a>
                or <a href="../api_reference/CXX/db.html" class="olink">Db</a> constructors. When this flag is on,
                all C++ methods fail by returning an error code rather
                than throwing an exception. 
            </p>
          </li>
          <li>
            <span class="bold">
              <strong>I get unexpected results and
                database corruption when running threaded
                programs.</strong>
            </span>
            <p>
                <span class="bold"><strong>I get error messages that mutex
                    (for example, pthread_mutex_XXX or mutex_XXX)
                    functions are undefined when linking applications
                    with Berkeley DB.</strong></span>
            </p>
            <p> 
                On some architectures, the Berkeley DB library uses
                the ISO POSIX standard pthreads and UNIX International
                (UI) threads interfaces for underlying mutex support;
                for example, Solaris and HP-UX. You can specify compilers or
                compiler flags, or link with the appropriate thread
                library when loading your application to resolve the
                undefined references: 
            </p>
            <pre class="programlisting">cc ... -lpthread ...
cc ... -lthread ...
xlc_r ...
cc ... -mt ...</pre>
            <p>
                See the appropriate architecture-specific Reference
                Guide pages for more information.
            </p>
            <p> 
                On systems where more than one type of mutex is
                available, it may be necessary for applications to use
                the same threads package from which Berkeley DB draws
                its mutexes. For example, if Berkeley DB was built to
                use the POSIX pthreads mutex calls for mutex support,
                the application may need to be written to use the
                POSIX pthreads interfaces for its threading model.
                This is only conjecture at this time, and although we
                know of no systems that actually have this
                requirement, it's not unlikely that some exist. 
            </p>
            <p>
                In a few cases, Berkeley DB can be configured to
                use specific underlying mutex interfaces. You can use
                the <a class="link" href="build_unix_conf.html#build_unix_conf.--enable-posixmutexes">
                --enable-posixmutexes</a> and <a class="link" href="build_unix_conf.html#build_unix_conf.--enable-uimutexes">--enable-uimutexes</a> 
                configuration options to specify the POSIX and Unix International (UI)
                threads packages. This should not, however, be
                necessary in most cases. 
            </p>
            <p>
                In some cases, it is vitally important to make sure
                that you load the correct library. For example, on
                Solaris systems, there are POSIX pthread interfaces in
                the C library, so applications can link Berkeley DB
                using only C library and not see any undefined
                symbols. However, the C library POSIX pthread mutex
                support is insufficient for Berkeley DB, and Berkeley
                DB cannot detect that fact. Similar errors can arise
                when applications (for example, tclsh) use dlopen to
                dynamically load Berkeley DB as a library.
            </p>
            <p> 
                If you are seeing problems in this area after you
                confirm that you're linking with the correct
                libraries, there are two other things you can try.
                First, if your platform supports interlibrary
                dependencies, we recommend that you change the
                Berkeley DB Makefile to specify the appropriate
                threads library when creating the Berkeley DB shared
                library, as an interlibrary dependency. Second, if
                your application is using dlopen to dynamically load
                Berkeley DB, specify the appropriate thread library on
                the link line when you load the application itself.
            </p>
          </li>
          <li>
            <span class="bold">
              <strong>I get core dumps when running
                programs that fork children.</strong>
            </span>
            <p>
                Berkeley DB handles should not be shared across
                process forks, each forked child should acquire its
                own Berkeley DB handles. 
            </p>
          </li>
          <li>
            <span class="bold">
              <strong>I get reports of uninitialized
                memory reads and writes when running software analysis
                tools (for example, Rational Software Corp.'s Purify
                tool).</strong>
            </span>
            <p> 
                For performance reasons, Berkeley DB does not write
                the unused portions of database pages or fill in
                unused structure fields. To turn off these errors when
                running software analysis tools, build with the <a class="link" href="build_unix_conf.html#build_unix_conf.--enable-umrw">--enable-umrw</a>
                configuration option.
            </p>
          </li>
          <li>
            <span class="bold">
              <strong>Berkeley DB programs or the test
                suite fail unexpectedly.</strong>
            </span>
            <p> 
                The Berkeley DB architecture does not support
                placing the shared memory regions on remote
                filesystems -- for example, the Network File System
                (NFS) or the Andrew File System (AFS). For this
                reason, the shared memory regions (normally located in
                the database home directory) must reside on a local
                filesystem. See <a href="../programmer_reference/env_region.html" class="olink">Shared memory region</a> for more information.
            </p>
            <p> 
                With respect to running the test suite, always
                check to make sure that TESTDIR is not on a remote
                mounted filesystem.
            </p>
          </li>
          <li>
            <span class="bold">
              <strong>The <a href="../api_reference/C/db_dump.html" class="olink">db_dump</a> utility fails to build.</strong>
            </span>
            <p> 
                The <a href="../api_reference/C/db_dump.html" class="olink">db_dump185</a> utility is the utility that supports the
                conversion of Berkeley DB 1.85 and earlier databases
                to current database formats. If the build errors look
                something like the following, it means the db.h
                include file being loaded is not a Berkeley DB 1.85
                version include file:
            </p>
            <pre class="programlisting">db_dump185.c: In function `main':
db_dump185.c:210: warning: assignment makes pointer from integer 
without a cast
db_dump185.c:212: warning: assignment makes pointer from integer 
without a cast
db_dump185.c:227: structure has no member named `seq'
db_dump185.c:227: `R_NEXT' undeclared (first use in this function)</pre>
            <p>
                If the build errors look something like the
                following, it means that the Berkeley DB 1.85 code was
                not found in the standard libraries: 
            </p>
            <pre class="programlisting">cc -o db_dump185 db_dump185.o
ld:
Unresolved:
dbopen</pre>
            <p>
                To build the <a href="../api_reference/C/db_dump.html" class="olink">db_dump185</a> utility, the Berkeley DB version
                1.85 code must already been built and available on the
                system. If the Berkeley DB 1.85 header file is not
                found in a standard place, or if the library is not
                part of the standard libraries used for loading, you
                will need to edit your Makefile, and change the
                following lines: 
            </p>
            <pre class="programlisting">DB185INC=
DB185LIB=</pre>
            <p>
                So that the system Berkeley DB 1.85 header file and
                library are found; for example: 
            </p>
            <pre class="programlisting">DB185INC=/usr/local/include
DB185LIB=-ldb185</pre>
          </li>
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